We plan to study the chemistry, metabolism and function of ribosomes and ribosomal RNA, as well as functionally related RNA such as messenger and transfer RNA. Emphasis will be placed on the components of the mitochondrial protein synthesizing system. These will be compared with homologous cytoplasmic and prokaryotic (in particular mycoplasmal) components, with the general aims of elucidating (1) the evolutionary status of the mitochondrial protein synthesizing system; (2) structure-function relationships among the various components; and (3) the role of mitochondrial biosynthetic activity in mitochondrial biogenesis and cell growth. Processing of ribosomal and messenger RNA will be examined with special attention given to the role and nature of minor nucleotides, including the ubiquitous Nz6methyladenine residue of small ribosomal sub-unit RNA and the methylated blocked 5'-end-groups of cytoplasmic mRNA. Preliminary experiments indicating that Sindbis virus-coded mRNA has a distinctive blocked 5'-end-group will be extended and refined. We shall employ mainly cultured animal cells, hamster (BHK) and human (HeLa). Our approach will include radioactive labeling of normal and infected cells; pulse- and pulse-chase studies; in vitro labeling of RNA for end-group analysis; electrophoretic and chromatographic analysis of RNA components released by acid, alkali and enzymatic digestion; oligonucleotide fingerprinting and sequence studies using the procedures of Sanger and Brownlee; in vitro studies of rRNA maturation using the E. coli processing enzyme RNase III; and effects of mitochondrial and other types of mRNA on in vitro protein synthesis.